1. Field of the Invention
The present invention relates generally to pumps and, more specifically, to a differential expansion control assembly for a pump in a transmission of a motor vehicle.
2. Description of the Related Art
It is known to provide a pump for a transmission in a motor vehicle. The pump may be of a variable or fixed displacement type. The pump generally includes a pump body and a pumping mechanism. Commonly, the pump body is made of an aluminum material because of its light weight and the pumping mechanism is made of a steel material because of its wear and friction properties.
It is also known that the thermal expansion coefficient for aluminum is greater than the thermal expansion coefficient for steel. As a result, the pump body expands more than the pumping mechanism as temperature increases, in turn, increasing internal clearances of the pump. Since the pump is designed to resist seizing at low temperatures (-40.degree. F.), additional clearance results at higher temperatures due to the differential expansion. As leakage is generally proportional to the cube of the clearance, this additional clearance is responsible for a large increase in pump leakage at normal operating temperatures (150.degree. to 250.degree. F.).